NMR spectroscopic identification of Ni(<scp>ii</scp>) species formed upon activation of (α-diimine)NiBr2 polymerization catalysts with MAO and MMAO

The nature of Ni(II) species formed upon the activation of the Brookhart&#39;s α-diimine polymerization pre-catalyst LNiBr2 with MAO and MMAO (L = 1,4-bis-2,4,6-dimethylphenyl-2,3-dimethyl-1,4-diazabuta-1,3-diene) has been established using 1H and 13C NMR spectroscopy. The heterobinuclear ion pair [LNiII(μ-Me)2AlMe2]+[MeMAO]− is observed at the initial stage of the reaction of LNiBr2 with MAO at −40 &#176;C, whereas the ion pair [LNiII–tBu]+[MeMMAO]− predominates at the initial stage of the reaction of LNiBr2 with MMAO under the same conditions. At higher temperatures, both ion pairs transform into a Ni(I) species displaying an axially anisotropic EPR spectrum (g‖ = 2.21, g⊥ = 2.06, A⊥ = 1.06 mT).